“The idea was to try to break a hole through to find the guys because there was no communication and no way of knowing if they were alive or where they were in the mine,” said Cementation Canada president Roy Slack. “All that was known was that both accesses underground were blocked off and there were 33 guys who were unaccounted for.”
Drilling a 5-inch hole from surface to a depth of 700 metres was “like finding a needle in a haystack,” said Slack. “It was very tricky business. The first holes drilled were surveyed and that gave them an idea of the deviation the rock was causing.”
Terraservice, a Chilean drilling company and partner of Cementation Canada, finally broke through on August 22 and hauled up a hand-scrawled note confirming that the 33 miners were alive after 17 days of confinement and dwindling food supplies.
Terracem, a Chilean company jointly owned by Terraservice and Cementation Canada, mobilized a Strata 950 raise borer to the site one day later and began drilling a 15-inch diameter pilot hole on September 1st. This effort, known as Plan A, was overseen by Glen Fallon, a Cementation Canada employee from North Bay.
Reluctant to put all their eggs in one basket, the Chilean government also brought two other groups in with different drilling technologies.
Plan B relied on a Schramm T130XD, a well drilling rig and drilling hammers from Center Rock Inc. of Berlin, Pennsylvania to widen one of the original five-inch holes. Plan C was carried out by Precision Drilling of Calgary, Alberta, using a massive oil-drilling rig.
t was the Plan B team that finally broke through with a 28-inch diameter hole on October 9, leading to the rescue of the miners on October 12 and 13 after 68 days underground.
The Plan A team ceased drilling at the 600-metre level when it became obvious that the Schramm T13XD was about to break through.
“We had about four days to break through but we didn’t want to because what happens with our drilling is that the 15-inch hole is full of water, so if we were to break through, 700 meters of water in that 15-inch hole would have gone into the mine and down the ramp,” explained Slack.
Even if the Plan A team had broken through first, it would have still been necessary to send down a reamer head to ream out the hole to a diameter of 28 inches, which would have taken an additional 30 days.
“It’s interesting because Plan B was the long shot,” said Slack. “The equipment wasn’t really sized for the job. It’s a hole opener that’s fine for going from eight to 12 inches, but they were trying to take it to 28 inches. The machine was at the extreme of its capability, but they decided to try it. They had a lot of challenges – they broke bits, they lost bits and they struggled with it, but they kept making progress, so they kept at it.”
Slack admits to having mixed emotions about losing the race to Plan B.
“First and foremost was to get those guys out as soon as possible, so while you’re hoping you’ll be the first to get down there, you’re also cheering on the other two teams as well.”
Normally, raise boring is used to drill a hole between two levels of a mine, or from surface to an accessible level underground. Once the drill breaks through to the target level, the bit is removed and a reamer head is attached to the drill string at the lower level. That wasn’t possible in this case because the underground level wasn’t accessible, so Cementation Canada worked with Atlas Copco to design a reamer head that could be sent down the pilot hole and assembled by the miners underground. Once assembled and joined to the drill string, the reamer head would have been drilled up towards surface to a diameter of 28 inches, allowing the broken rock, or fines, to fall down through the hole.
“Once the (reamer head) design was put on paper, we looked at fabricators who did this type of work – one in Australia, one in the U.S., one in South Africa and one in Canada. Mining Technologies International in Sudbury offered the quickest turnaround globally,” said Slack.
The reamer head was manufactured with the assistance of Sudbury-based Bristol Machine Works, but was never deployed.
“What we have to do now is step back from this and make sure something like this never happens again,” said Slack.
With communication and tracking technology in place, he acknowledged, family members wouldn’t have had to wait 17 days to find out if their loved ones were dead or alive and rescuers would have known their exact whereabouts.
“Knowing they were alive and where they were, the rescue could have started right away.”
The Chilean mine disaster also serves as a reminder that the secondary means of egress needs to be properly maintained and accessible, said Slack.